Friday, January 23, 2009

The Namib Desert - Great Geology!

Our private jet trip has resumed with a four hour flight across the equator and on to the country of Namibia (the former South West Africa). With a population of less than 2 million but the size of Texas and Louisiana combined, it is the second least densely populated country on earth (after Mongolia). But to the geologist it is a paradise! Look at the pics.
This is the "moon landscape" as they call it in Nmibia, located near the coastal town of Swakopmund. It is a tortured land and banded gneiss, and only a few millimeters of rain per year. We toured this area in vans.

Here is a pretty good look at an outcrop of gneiss. This metamorphic rock formed about 600 million years ago when sediments were crushed and buried in a great mountain building event.

The gneiss rocks were probably at quite a depth (15 miles?) to be cooked this much. But below them, things were even hotter and some of those rocks were melted to become magma, which traveled upwards into the gneiss as magma. When these dikes were emplaced they were likely very tabular in shape but continued squeezing and crushing caused them to take this contorted shape. Imagine the amount of material eroded to bring all of this back to the surface today!

Here is further evidence of the extreme compression of the rocks. When the Kalahari craton collided with the Congo craton some 600 Ma, it created the Damara mobile belt, essentially the area between the two that was 'bruised" in the collision. Wow - it's a living planet!

This is the graphic I used on the jet to explain the concept of two continental fragments colliding to create a mobile belt. Notice the two cratons (light colored areas) and the collision zone between them. Swakopmund and the moon landscape are in the dark belt near the town of Walvis Bay.

1 comment:

Chris Clarke said...

Would you consider submitting this wonderful post to the upcoming Carnival of the Arid?